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Science (086) — AI-generated practice question

AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.

Q1. [1] medium exam-ready
Stars twinkle at night but planets do not. The most accurate reason for this difference is:
  1. A Planets emit their own light while stars do not
  2. B Planets are much closer to Earth and act as extended sources, so light variations average out
  3. C Stars are hotter than planets and so their light fluctuates more
  4. D Planets move faster across the sky, reducing the twinkling effect
Generated by claude-sonnet-4-6 · 2026-06-26 01:07 · grounding rag
Model Answer

Answer: B

Planets are much closer to Earth and act as extended sources of light, so the fluctuations in light from individual point-sized sources average out to zero, nullifying the twinkling effect.

Source: Chapter 10, Section 10.5 – Atmospheric Refraction

Explanation

The textbook explicitly states that planets, being closer, appear as extended sources (collection of many point-sized sources), and the total variation in light entering the eye averages out to zero. Stars, being very distant, act as point sources, so atmospheric refraction causes their light to flicker — producing twinkling. Option A is wrong (planets reflect light, not emit); C and D have no textual or scientific basis.

Previous-year CBSE Grade 10 board exam questions, organised by subject and chapter, each with a model answer — free to read and print.